1. Technical Field
The present invention relates to an atomic force microscope (hereinafter, referred to as “AFM”) probe, and more particularly, to an AFM cantilever having a nanoindentation testing function.
2. Description of Related Technology
Up to now, attempts to manufacture a variety of elements and parts using the nano technology have been actively made. The size of products manufactured with use of the nano technology is generally less than hundreds of nanometers. To predict mechanical properties of such products and develop design technologies, the technique for measuring mechanical properties of a test specimen whose size is less than hundreds of nanometers is required. Nanoindentation tests are very useful as methods of measuring the mechanical properties of the test specimen whose size is within a range of nanometers. Since such a nanoindentation testing function is employed in the AFM technologies that are under rapid development, attempts to measure mechanical properties such as elastic modulus and hardness of a small-sized test specimen that has never been measured even by any conventional tester can be made.
Some commercial AFM products having a nanoindentation testing function are sold. FIG. 1 schematically shows an AFM cantilever portion of the conventional AFM having an indentation testing function. The general AFM cantilever and AFM tip are made of silicon, whereas the AFM cantilever having a nanoindentation testing function is made of stainless steel and the AFM tip mounted thereon is made with diamond. One end of the AFM cantilever 10 is fixed to a fixed stage 40 and the other end of the AFM cantilever 10 becomes a free end. The AFM tip 20 is attached to a surface of the other end of the AFM cantilever 10, and a mirror 30 is mounted on the opposite surface thereof. Further, a light source (not shown) for illuminating light 70, such as laser, to the mirror 30 and a light-receiving element (not shown) for receiving light reflected from the mirror are provided to a main body of the AFM. A test specimen 60 to be measured is mounted on an xyz scanner 50 below the AFM tip 20 to be in contact with the AFM tip 20, so that the surface shape and mechanical property of the test specimen 60 are measured.
An indentation testing process for measuring the mechanical properties of the test specimen 60 using the conventional AFM shown in FIG. 1 will be described with reference to FIG. 2. When the xyz scanner 50 with the test specimen 60 mounted thereon is raised from a state “a” to a state “b” (in a z-axis direction), the AFM cantilever 10 is also displaced from a state “A to a state “B”. Accordingly, a contact surface of the test specimen that is in contact with the AFM tip 20 is indented and deformed by the AFM tip 20. (On the other hand, it may be configured in such a manner that the xyz scanner 50 with the test specimen 60 mounted thereon is fixed and the fixed stage 40 with the AFM cantilever 10 fixed thereto is moved.) An amount of displacement of the AFM cantilever 10 is measured by detecting a light-receiving position of the light 70 reflected from the mirror 30 using the light-receiving element such as a photodiode, and an amount of indentation deformation of the test specimen is accordingly calculated from the difference between the amount of displacement of the AFM cantilever 10 and the amount of movement of the xyz scanner in the z-axis direction. At the moment, as shown in FIG. 2, the AFM tip is subject to a lateral motion x0 as well as a vertical motion z0 due to the inherent structure of the AFM cantilever 10. The general AFM is designed to measure the surface shape of the test specimen, and the lateral motion generated upon the vertical motion of the AFM cantilever is not issued. If the nanoindentation testing function is added to the conventional AFM, however, the unnecessary lateral motion in addition to the desired vertical indentation motion are generated in the AFM cantilever due to mechanical characteristics of the AFM cantilever. Therefore, the following several problems occur. That is, since the lateral motion becomes a significant error factor in the measurement of the mechanical properties of the specimen, some compensation for the lateral motion should be made such that the exact measuring results for the amount of indentation deformation of the test specimen can be obtained.
To compensate for the lateral motion, the conventional AFM may be operated as shown in FIG. 3. That is, when the test specimen 60 is subject to the lateral indentation deformation, the xyz scanner 50 is allowed to move the test specimen 60 in the horizontal direction by the amount x0, so that the influence of the lateral motion can be removed. The removal of the lateral motion influence in such a manner may involve a variety of problems such as vibration occurring upon the movement of the test specimen 60, an error in the amount of movement of the test specimen, and a synchronization error between the lateral indentation motion and the test specimen movement, which in turn cause uncertainty of the measurement results to increase. In addition, the AFM cantilever of the conventional AFM is further bent on the fixed end during the indentation test. Therefore, when an indentation depth is calculated, the motion of the AFM tip positioned at the end of the cantilever should be assumed from the geometric shape of the AFM cantilever and tip. However, geometric uncertainty induced when manufacturing the AFM cantilever and tip becomes a significant error factor in the calculation of indentation depth. Since the indentation depth is a raw data that is very important in the physical property measurement, it also causes errors in the physical property measurement results. Therefore, to measure the mechanical property of the test specimen more accurately using the AFM, the aforementioned problems that may be produced in the nanoindentation test using the conventional AFM must be solved.